α integrin cytoplasmic tails can rescue the loss of Rho-family GTPase signaling in the C. elegans somatic gonad

Abstract

Integrin signaling relies on multiple, distinct pathways to impact a diverse set of cell behaviors. The Rho family of GTPases are well-established downstream signaling partners of integrins that regulate cell shape, polarity, and migration. The nematode C. elegans provides a simple in vivo system for studying both integrins and the Rho family. Our previous work showed that the C. elegans α integrin cytoplasmic tails have tissue-specific functions during development. Here, we use chimeric α integrins to show that the cytoplasmic tails can rescue the loss of the Rho family of GTPases in three cell types in the somatic gonad. Knockdown of rho-1 by RNAi causes defects in sheath cell actin organization, ovulation, and vulva morphology. Chimeric α integrin ina-1 with the pat-2 cytoplasmic tail can rescue both actin organization and ovulation after rho-1 RNAi, yet cannot restore vulva morphology. Knockdown of cdc-42 by RNAi causes defects in sheath cell actin organization, ovulation, vulva morphology, and distal tip cell migration. Chimeric α integrin pat-2 with the ina-1 cytoplasmic tail can rescue vulva morphology defects and distal tip cell migration after cdc-42 RNAi, yet cannot restore sheath cell actin organization or ovulation. Disruption of Rac yields the same phenotype in distal tip cells regardless of α integrin cytoplasmic tail composition. Taken together, the cytoplasmic tails of α integrins can bypass signaling from members of the Rho family of GTPases during development.

Two distinct myosin II populations coordinate ovulatory contraction of the myoepithelial sheath in theCaenorhabditis eleganssomatic gonad

“…Previous work showed that C. elegans RHO-1 is essential for ovulation and fertility ( Norman et al. , 2005 ; McMullan and Nurrish, 2011 ; Meighan et al. , 2015 ), but its downstream effectors in ovulation have not been identified.…”

Myosin activity drives actomyosin bundle formation and organization in contractile cells of theCaenorhabditis elegansspermatheca

“…, 2004 ; McMullan and Nurrish, 2011 ; Kovacevic et al. , 2013 ; Meighan et al. , 2015 ; Ono and Ono, 2016 ), which cooperate to increase phosphorylation of the myosin regulatory light chain (p-MRLC) and actomyosin contractility in smooth muscle and nonmuscle cells ( Somlyo and Somlyo, 2000 ).…”

“…In both tissues, RHO-1/RhoA signaling activates Rho-associated kinase, LET-502/ROCK, which phosphorylates and inactivates the myosin-associated phosphatase regulatory subunit MEL-11 (referred to here as myosin phosphatase), leading to increased p-MRLC ( Wissmann et al. , 1999 ; McMullan and Nurrish, 2011 ; Meighan et al. , 2015 ; Ono and Ono, 2016 ).…”

Development and maintenance of functional actomyosin networks

“…RhoA signaling pathways (Clandinin et al, 1998;Wissmann et al, 1999b;Bui and Sternberg, 2002;Kariya et al, 2004b;Yin et al, 2004;McMullan and Nurrish, 2011;Kovacevic et al, 2013;Meighan et al, 2015;Ono and Ono, 2016a) that cooperate to increase phosphorylation of the myosin regulatory light chain (p-MRLC) and actomyosin contractility in smooth muscle and nonmuscle cells (Somlyo and Somlyo, 2000). In the C. elegans gonad, two phospholipase C isoforms, Cg (PLC-3) and Ce (PLC-1), cleave phosphatidyl inositol to produce inositol 1,4,5triphosphate (IP 3 ), which triggers Ca 2+ release from the endoplasmic reticulum (Clandinin et al, 1998;Bui and Sternberg, 2002;Kariya et al, 2004b;Yin et al, 2004;Kovacevic et al, 2013).…”

“…This likely increases myosin activity by activating a Ca 2+ -calmodulin dependent myosin light chain kinase (Adelstein, 1982;Somlyo and Somlyo, 2000). In both tissues, RHO-1/RhoA signaling activates Rho-associated kinase, LET-502/ROCK, which phosphorylates and inactivates the myosin-associated phosphatase regulatory subunit, MEL-11 (referred to here as myosin phosphatase), leading to increased p-MRLC (Wissmann et al, 1999b;McMullan and Nurrish, 2011;Meighan et al, 2015;Ono and Ono, 2016a). However, unlike sheath cells, spermathecal cells lack the troponin-tropomyosin complex (Ono and Ono, 2004;Ono et al, 2007) responsible for Ca 2+ regulation of actomyosin contraction in muscle cells (Ebashi, 1984).…”